1. Field of the Invention
The present invention relates to a flow rate detector mechanism with a variable venturi therein for changing the value of constant flow rate with continuity, being suitable to be applied to a constant volume sampler (CVS) for diluting and sampling the exhaust gas discharged from an automobile, and further to an exhaust gas sampling method, in which the exhaust gas is diluted corresponding to the traveling mode patterns for evaluation test, using such the CVS as mentioned above wherein the variable venturi flow rate detector mechanism is applied, so as to sample the exhaust gas in a sampling bag.
2. Description of Related Art
For measuring weight of components in the exhaust gas emitted from an automobile, a sampling apparatus called a xe2x80x9cconstant volume sampler (CVS)xe2x80x9d is used as shown, for example, in Japanese Laid-Open Patent No. Sho 54-71689 (1979) and Japanese Laid-Open Patent No. Sho 54-127388 (1979).
Further, in Japanese Laid-Open Patent No. Sho 55-65133 (1980) is described the CVS for sampling a portion of diluted gas to be analyzed, being formed at a constant flow rate, by diluting a target gas such as the exhaust gas from the automobile with fresh air, in which a constant volume pump is driven by a synchronous motor so as to form a constant flow rate of the diluted gas.
In Japanese Laid-Open Patent No. Sho 62-157547 (1987), there is described a modal mass analysis method, according to air dilution of exhaust gas from the automobile, for increasing the accuracy in analyzing the emitted amounts of components in each mode of travel, in which the flow rate of exhaust gas obtained through the air dilution method is compensated by concentration of the target components corresponding to the same phase, being obtained through interpolation. Further, in the FIG. 1 of the publication thereof is described the CVS in which the constant volume venturi and a constant volume blower are connected in series.
In Japanese Laid-Open Patent No. Hei 4-216435 (1992), there is described an exhaust gas sampling apparatus for an internal combustion engine, in particular applying the CVS (Constant Volume Sampler) method thereto for improving the accuracy and also the response in the measurement. This exhaust gas sampling apparatus for an internal combustion engine is constructed in the following manner. Within a conduit, in which flows the diluted exhaust gas being formed by mixing the exhaust gas discharged from the internal combustion engine with fresh air, is positioned a sampling conduit for sampling a portion of the diluted exhaust gas. Connected to the sampling conduit are provided a suction pump, a critical venturi, an exhaust gas analyzer, and a throttle valve, in a sequence from the downstream side of the diluted exhaust gas. Further, between the critical venturi and the exhaust gas analyzer, there is provided a passage for introducing atmospheric air into the sampling conduit. With the provision of the passage for introducing the atmospheric air into the sampling conduit, fluctuation of the pressure in an exhaust gas analyzer is suppressed to be minute or very small even when the pressure rises in the conduit in which the diluted exhaust gas flows, thereby improving the response characteristic thereof. Further, the amount of change in the pressure within the exhaust gas analyzer is small even when a large volume of the diluted exhaust gas is introduced into the conduit, thereby having no influence on the accuracy in the measurement thereof.
Further, in Japanese Laid-Open Patent No. Hei 4-216435 (1992), with provision of an flow rate integrator in an air supply conduit, there is described an exhaust gas analyzer in which a standard total passage volume at a moment can be calculated in a calculation unit by taking into consideration the pressure and temperature of gas. This exhaust gas analyzer is constructed in the following manner. A sample-taking conduit is provided, into which the mixture of the exhaust gas and fresh air is supplied through a gas intake conduit, and a gas supply pump is positioned after the gas intake conduit. The gas supply pump is constructed with a rotation pump having a constant suction capacity, for example, and a critical nozzle is positioned before the rotation pump. In the air supply conduit is provided the flow rate integrator which is constructed with a vortex flow meter (a mass flow meter based on a principle such as Karman""s vortex). The output of the flow rate integrator is provided to the calculation unit. The calculation unit obtains the standard total passage volume at a moment by taking into the consideration the pressure and temperature of gas from the flow rate in the air supply conduit.
In the analysis of components in the exhaust gas with use of the CVS method in this manner, there is a necessity to alter the flow rate of the diluted gas depending upon the test modes. For example, in a cold transient (CT) phase starting from a time point when engine is started to a time point 505 seconds later, the flow rate of the diluted gas is determined to be 15 m3/min, and in a cold stabilizing (CS) phase from 505 sec to 1374 sec to be 3 m3/min. Further, after being stopped for ten (10) minutes from the time point at 1374 sec, the engine is re-started, and in a hot transient (HT) phase the flow rate of the diluted gas is determined to be at 3 m3/min.
For altering or exchanging the flow volume of diluted gas depending upon the test modes, according to the CVS of the conventional art, a plurality of systems are provided in parallel, in each of which valves for opening and closing and a fixed venturi are connected in series, wherein the one fixed venturi of the desired flow rate is selectively used. Thus, the plurality of systems of the fixed venturis through which the diluted gas flows are switched between based on the flow rates thereof.
FIG. 16 shows problems arising when the flow rate of the diluted gas is altered in the CVS device of the conventional art. As shown in FIG. 16(a), when the flow rate of the diluted gas is altered from 15 m3/min to 3 m3/min by, for example, turning from a condition where the first open/close valve 102 connected to the fixed venturi 101 in series is turned OPEN thereby conducting the diluted gas at the flow rate of 15 m3/min into a condition where the second open/close valve 104 of the flow rate of 3 m3/min, connected to the second venturi 103 in series, is turned OPEN while turning the first open/close valve 102 CLOSED, as shown in FIG. 16(b), time delay (i.e., a region with hatching lines) occurs in the time sequence during which the flow rate of the diluted gas is altered from 15 m3/min to 3 m3/min, and disturbance in the flow rate occurs.
In the portion (in the hatched area) of the time delay in the flow rate, the flow rate of the diluted gas is larger than the desired one, i.e., 3 m3/min, however in the conventional exhaust gas analysis with use of the CVS device, since the decreased volume of the exhaust gas in the flow rate during the time delay portion (the hatched area) is not reflected upon the analysis data, an error occurs in the result of analysis of the exhaust gas components, for example, in the degree of 0.3%. Further, since the disturbance occurs after the exchange of the flow rate, it sometimes also results in decrease in accuracy of the analyzed result.
Then, with provision of a flow meter in the passage for the diluted gas for measuring the flow rate thereof continuously, it can be considered that the measured flow rate of the diluted gas is reflected in the analyzed result thereof, thereby preventing any error therein from occurring. However, the provision of the flow meter in the passage for the diluted gas not only makes the apparatus itself large in size and expensive in cost thereof, but also increases the resistance in the passage for the diluted gas. Thus, the capacity of the blower must be larger for sucking the diluted gas, and therefore this is not a wise plan or design.
Therefore, a first object of the present invention, for dissolving such the problems as mentioned above, is to provide a flow rate detector mechanism using variable venturi therein, being able to alter or exchange the flow rate with continuity by changing the cross-sectional area of a throat, so as to eliminate the disturbance occurring upon the change in the flow rate of the diluted gas, and also to enable output the flow rate data with high accuracy even when the flow rate is altered but without provision of a flow meter as described above.
Japanese Laid-Open Patent No. Sho 54-127388 (1979) discloses the following, in connection with the measurement of components of the exhaust gas.
In general, the measurement of components in the exhaust gas is practiced by measuring the concentration of the gas components in the exhaust gas that is sampled in a bag within a predetermined time period, by means of the CVS device. As a method for measuring the gas concentration of components in the exhaust gas sampled in the bag, there is known a continuous measurement method for diluted gas, by which the gas concentration of the components can be obtained as an average concentration of the gas sampled as a whole and can be measured in a moment. In this continuous measurement method for diluted gas, the gas concentration of specific component(s) in sampling gas, being sampled from the exhaust gas which is diluted with the air continuously, is measured by a continuous detector, and instantaneous weight of the gas components is calculated by computation using the measured concentration and the flow rate of the sampled gas. However, the dilution ratio comes to be one per several tens (1/several tens) depending upon the operating condition of a car (in particular, in an idling operation). In explanation, with this method, the concentration of the sample gas is decreased too much, therefore, the detector for measuring the concentrations is required to be one which has high sensitivity. Furthermore, since the concentration of the sample gas come to be low (or lean), it is impossible to measure the concentration with high accuracy, due to error and so on being caused by changes in the concentration of the target components to be measured, which are contained in the air for use in dilution thereof.
In Japanese Laid-Open Patent No. Hei 4-268440 (1992) is described an analyzer for exhaust gas of automobiles, in which the exhaust gas discharged from the engine of an automobile is diluted with a gas for dilution, at the gas being diluted at a constant rate and such that the dilution ratio provides that no dew is condensed therein, to the diluted gas then being supplied to an analyzer portion as the sampling gas.
Further, in particular in the section describing the conventional arts in Japanese Laid-Open Patent No. Hei 4-268440 (1992), it is described that, for quantitative analysis of the components contained within the exhaust gas, the exhaust gas is sampled as the sample gas with use of the CVS, during which the automobile is operated on a chassis dynamo in accordance with a driving mode, such as a 10 mode, a LA-4C/H mode, etc., to be supplied to an analyzer portion of FTIR (Fourier Transform Infrared Spectrometer).
Further, in the section describing the conventional arts in Japanese Laid-Open Patent No. Hei 4-268440 (1992), it is described that the components and the average value of concentration thereof in the diluted gas can be obtained during a certain time period, by supplying the diluted gas into an analyzer portion, which is sampled in the bags for sampling dilute gas. Further, it is also described that the result of analysis can be obtained more correctly by having measured background values in advance through analysis of the air which was sampled in the air sampling bag.
Moreover, in the description of the problems to be dissolved by the invention of Japanese Laid-Open Patent No. Hei 4-268440 (1992), it is described that since the exhaust gas is obtained through burning of organic compounds including gasoline, carbon, and hydrogen, the exhaust gas contains water vapor therein, and when the water vapor is condensed into dew, the components of the gas are reduced because they dissolve into the water condensed from the vapor. Consequently, as a means for avoiding such situations, it is described that (1) the temperature of tunnels for dilution and gas passages are maintained to be higher than a certain value, so as to prevent the exhaust from being decreased in temperature thereof, and (2) the dilution rate (multiplying factor) of the diluted gas is increased by means of the air for dilution, so as to increase the dew point.
Also, in Japanese Laid-Open Patent No. Hei 8-226879 (1996), there is described a gas sampling apparatus wherein for diluting the exhaust gas discharged from a source of exhaust gas to be sucked in by the CVS, a sampling bag device is provided in a gas sampling flow passage divided from the CVS through a suction pump and a flow rate controller device, and wherein the gas sampling flow passage is heated in the region reaching up to the sampling bags in such a degree that the moisture in gas passing therethrough is not condensed, so as to provide for measurement of components included within the exhaust gas with high accuracy, while sampling the exhaust gas being diluted at the minimum limit.
However, in the exhaust gas sampling method for analyzing the components of the diluted gas being sampled in a sampling bag, the diluted gas must be set at such a dilution ratio that no condensation of moisture occurs in the diluted gas. By increasing the flow rate of the CVS (i.e., setting the dilution ratio at a high value), it is possible to protect the diluted gas from the condensation of moisture therein. However, if the dilution ratio is increased, the influences of CO, HC, NOx, and so on contained in the fresh air from outside become large, and therefore it is difficult to obtain the analysis data correctly.
Turning attention to the discharged volume of the exhaust gas in each of phases within the traveling modes, the dilution rate is decreased by making the CVS different in the flow rate thereof in each of the phases, so as to obtain the correct analysis data.
FIG. 12 and FIG. 13 are graphs showing the results of measurements in a case where the CVS flow rate is changed for each of the phases wherein, in particular, FIG. 12 shows a relationship between the flow rate of the exhaust gas in the LA-4 mode, while FIG. 13 shows the dew point in the gas sampling bag. The LA-4 mode comprises the CT phase from start of the measurement up to 505 sec, the CS phase from 505 sec up to 1,374 sec, and the HT phase starts after a 600 sec pause up to 505 sec thereafter (note that the HT phase is similar to the CT phase, and therefore is eliminated in FIGS. 8, 9, 10, 12, 13, 14, and 15). The traveling patterns, including operation states such as acceleration, constant speed, deceleration, etc. (speed patterns of automobiles), are set up corresponding to the development of time. In FIGS. 12 and 13, the traveling pattern indicates the speed (vehicle speed) of the automobile running on the chassis dynamo equipment, for testing. In FIG. 12, the flow rate of exhaust gas indicates the measured value of exhaust gas of the automobile running on the chassis dynamo equipment. The test condition shown in FIG. 12 is that the CVS flow rate in the CS phase is set at 2.4 m3/min, while the CVS flow rate is set at 1.6 m3/min. The sampling bags are heated at 40xc2x0 C. in temperature thereof.
For such a condition, the change in the dew point within the gas sampling bag is shown in FIG. 13 in particular, using the case of a gasoline car as an example, when a portion of the exhaust gas (the diluted gas) which is diluted by means of the CVS is sampled in the gas sampling bags. In the CT phase in which the CVS flow rate is set at 2.4 m3/min, the peak value of the dew point within the bag is 34.6xc2x0 C. (at the dilution ratio of 3.34), however, the dew point within the bag is decreased to 32.6xc2x0 C. (at the dilution ratio of 3.95) in the final stage of the CT phase. In the same manner, in the CS phase in which the CVS flow rate is set at 1.6 m3/min, the peak value of the dew point within the bag is 36.0xc2x0 C. (at the dilution ratio of 2.29), however, the dew point within the bags is decreased to 31.5xc2x0 C. (at the dilution ratio of 4.34) in the final stage of the CS phase.
Under the condition mentioned above, since the sampling bag is heated to 40xc2x0 C. in temperature thereof, no dew is condensed as long as the dew point within the sampling bag (BAG) is less than 40xc2x0 C. In the measured results of the dew points within the bag shown in FIG. 13, because there still remains a margin up to 40xc2x0 C., it can be considered that the diluted gas may be sampled in the sampling bag by changing the CVS flow rate down to a lesser value (i.e., by decreasing the dilution ratio), so as to sample in the sampling bag the diluted gas which is higher or richer in the exhaust gas condensation.
FIGS. 14 and 15 show the measured results of the CVS flow rates in a case where the condition is lower than those shown in FIGS. 12 and 13. In particular, FIG. 14 shows a relationship between the flow rate of exhaust gas and the CVS flow rate, and FIG. 15 shows the dew point within the sampling bag. As shown in FIG. 14, when the CVS flow rate is set at 1.84 m3/min in the CT phase and the flow rate is set at 1.35 m3/min in the CS phase, the peak values of the dew point within the bag come to be 38xc2x0 C. in both the CT phase and the CS phase, and the final dew point within the bag to be 35.8xc2x0 C. in the CT phase and 33.3xc2x0 C. in the CS phase, as shown in FIG. 15, thereby enabling bringing them closer to the heating temperature of the sampling bag. However, as shown in FIG. 14, the flow rate of exhaust gas sometimes exceeds the CVS flow rate in the case where the CVS flow rate is set at 1.84 m3/min in the CT phase and the flow rate at 1.35 m3/min in the CS phase, and therefore it is impossible to perform the measurement correctly.
Therefore, another object according to the present invention, for dissolving such problems as mentioned above, is to provide an exhaust gas sampling method in which the diluted gas at a low dilution ratio can be sampled in the sampling bag while preventing the condensation of moisture therein, by changing the CVS flow rate corresponding to the traveling mode patterns for evaluation testing of the exhaust gas, and the diluted gas of the low dilution ratio (the diluted gas in a condition of high exhaust gas concentration) can be sampled in the sampling bag by bringing the peak value of the dew point in the bag and the final dew point in the bag towards the peripheral temperature of the bags, thereby increasing the accuracy in analysis of the exhaust gas components.
According to the present invention, for achieving the first object of the invention mentioned above, there is provided a flow rate detector mechanism using variable venturi therein, comprising:
a variable flow rate generator, comprising:
a core; and
a variable critical flow venturi;
wherein a throat cross-sectional area defined between the core and the variable critical flow venturi may be changed by shifting relative positions of the core and the variable critical flow venturi in a direction of axes thereof;
the flow rate detector mechanism further comprising a flow rate calculation processing portion for calculating a flow rate on basis of the relative positions in the direction of the axes thereof and for outputting the calculated flow rate.
With the flow rate detector mechanism using variable venturi therein, since it is possible to change the value of constant flow rate continuously, no disturbance occurs in the value thereof when the flow rate is altered. Further, with the flow rate detector mechanism using variable venturi therein, according to the present invention, it is possible to output the flow rate value even when the flow rate is altered. Accordingly, upon analyzing the exhaust gas components, it is possible to reflect the change in the flow rate, occurring when the flow rate is altered, in the analysis data, thereby outputting the result of analyzing correctly. Accordingly, with using the flow rate detector mechanism using variable venturi therein, according to the present invention, no error is contained in the result of analysis even when the flow rate of the diluted gas is altered corresponding to the test modes, thereby the results of analysis may be obtained with high accuracy.
Next, according to the present invention, for achieving the second object mentioned above, there is provided an exhaust gas sampling method for analyzing exhaust gas of an automobile, using a flow rate detector mechanism using variable venturi therein, comprising the following steps:
diluting the exhaust gas from the automobile with fresh air from outside;
sampling a portion of the diluted exhaust gas into a sampling bag at a certain ratio; and
analyzing the diluted exhaust gas being sampled, wherein a flow rate through said flow rate detector mechanism is changed in a phase of mode for measurement, so that at least a final dew point in the sampling bag approaches a predetermined temperature within a predetermined temperature range.
Further, according to the present invention, it is preferable that the flow rate through said flow rate detector mechanism is changed in the phase of mode for measurement, so that the dew point in the sampling bag is averaged. Also, the flow rate through said flow rate detector mechanism is changed in the phase of mode for measurement, so that at least the flow rate through said flow rate detector mechanism does not exceed the flow rate of the exhaust gas during the measurement. Furthermore, it is preferable to change the flow rate of the sampling gas depending upon a change in the flow rate through said flow rate detector mechanism.
Applying the exhaust gas sampling method according to the present invention, it is possible to make small the difference between the peak value in the dew point within the bag and the final dew point within the bag, as well as to cause the final dew point to approach the temperature at which the bag is maintained. Accordingly, it is possible to lower the dilution ratio at the final dew point within the bag, as well as to improve the accuracy of the analysis.